Transducer-induced heating-facilitated cleaning

ABSTRACT

In described examples, a transducer vibrates a lens element in a heating mode and a cleaning mode. Controller circuitry activates the transducer in the heating mode in response to an estimated temperature, and activates the transducer in the cleaning mode after the transducer is activated in the heating mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/463,840 filed Feb. 27, 2017, which is incorporatedherein by reference in its entirety.

This application is related to coassigned U.S. patent application Ser.No. 15/887,923 filed Feb. 2, 2018 and coassigned U.S. patent applicationSer. No. 15/903,569 filed Feb. 23, 2018, which are incorporated hereinby reference in their entireties.

BACKGROUND

Electronic optical sensors are widely used for generating electronicimages. Often, such sensors (e.g., “cameras”) are located in placesremote to a viewer. The remote locations include places (e.g., externalto vehicles) where contaminants (e.g. moisture and/or dirt) from theenvironment can cloud or otherwise obscure the camera lens, such thatdegraded images are generated by a camera having an obscured lens. Thedegradation of the image quality can decrease safety or security in manyapplications. Various techniques for automatically cleaning the cameralenses include water sprayers, mechanical wipers, or air jet solutions.Such approaches are not practical or too costly in a variety ofapplications.

SUMMARY

In described examples, a transducer vibrates a lens element in a heatingmode and a cleaning mode. Controller circuitry activates the transducerin the heating mode in response to an estimated temperature, andactivates the transducer in the cleaning mode after the transducer isactivated in the heating mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example computing device for controllinga transducer coupled to a lens element.

FIG. 2 is a cross-section view of an example camera lens cover system.

FIG. 3 is a waveform diagram of an impedance response of an examplecamera lens cover system over a broad frequency range.

FIG. 4 is a waveform diagram of an impedance response of an examplecamera lens cover system over a reduced frequency range.

FIG. 5 is a plot diagram showing a linear relationship between theimpedance response of an example camera lens cover system and operatingtemperatures thereof while operating at a selected operating frequencyof 20 kHz.

FIG. 6 is a flow diagram of an example process for estimating atemperature of an example camera lens cover system in response to animpedance measurement of the example camera lens cover system.

FIG. 7 is an isometric view of an example camera lens cover system.

FIG. 8 is an external view of example foreign contaminant volumes for anexample camera lens cover system.

FIG. 9 is a block diagram of an example signal generator of an examplecamera lens cover system.

FIG. 10 is a flow diagram illustrating an example method of foreigncontaminant removal from an exposed surface of the example camera lenscover system.

FIG. 11 is a waveform diagram of impedance and phase response of anexample camera lens cover system over a broad frequency range.

FIG. 12 is a top view of an example vehicle including example cameralens cover systems.

DETAILED DESCRIPTION

In this description: (a) the term “portion” means an entire portion or aportion that is less than the entire portion; (b) the term “housing”means a package or a sealed subassembly/assembly, which can includecontrol circuitry, a transducer, lenses and an imaging sensor in a localenvironment that is sealed from an outside environment.

Ultrasonic vibration of lens surfaces (including lens covers) of camerasystems (e.g. automotive systems including rear view and/or surroundview systems) can be more cost effective than various water sprayer,mechanical wiper, or air jet solutions. As described herein,piezoelectric transducers (e.g., within a camera housing) can bemonitored in a feedback loop structure without including a thermocouplein the feedback loop. The piezoelectric transducer is controlled byestimating a temperature of a piezoelectric transducer, such that, forexample, the buildup of heat (which can be caused by activating thepiezoelectric transducer) is limited by a comparison to a temperaturethreshold. The limiting of the buildup of heat helps prevent thepermanent depolarization of the piezoelectric transducer (e.g., whichcould adversely affect the ability of the piezoelectric transducer tovibrate).

The apparatus and methods described herein for controlling and operatinga piezoelectric transducer can help ensure that the temperature of thepiezoelectric transducer does not reach more than one-half a Curietemperature (in degrees Celsius) of the piezo material of the transducerbeing controlled. In example embodiments, the transducer lifetime can beextended by the avoidance of operating the piezoelectric transducer atpotentially damaging temperatures.

FIG. 1 is a block diagram of a computing device 100 for controlling atransducer coupled to a lens element. For example, the computing device100 is, or is incorporated into, or is coupled (e.g., connected) to anelectronic system 129, such as a computer, electronics control “box” ordisplay, controllers (including wireless transmitters or receivers), orany type of electronic system operable to process information.

In example systems, a computing device 100 includes a megacell or asystem-on-chip (SoC) that includes control logic such as a centralprocessing unit (CPU) 112, a storage 114 (e.g., random access memory(RAM)) and a power supply 110. For example, the CPU 112 can be a complexinstruction set computer (CISC)-type CPU, reduced instruction setcomputer (RISC)-type CPU, microcontroller unit (MCU), or digital signalprocessor (DSP). The storage 114 (which can be memory such ason-processor cache, off-processor cache, RAM, flash memory, or diskstorage) stores one or more software applications 130 (e.g., embeddedapplications) that, when executed by the CPU 112, perform any suitablefunction associated with the computing device 100. The processor isarranged to execute code (e.g., firmware instructions and/or softwareinstructions) for transforming the processor into a special-purposemachine having the structures—and the capability of performing theoperations—described herein.

The CPU 112 includes memory and logic circuits that store informationthat is frequently accessed from the storage 114. The computing device100 is controllable by a user operating a UI (user interface) 116, whichprovides output to and receives input from the user during the executionthe software application 130. The UI output can include indicators suchas the display 118, indicator lights, a speaker, and vibrations. The UIinput can include sensors for receiving audio and/or light (using, forexample, voice or image recognition), and can include electrical and/ormechanical devices such as keypads, switches, proximity detectors,gyros, and accelerometers. For example, the UI can be responsive to avehicle operator command to clear an exterior surface of a backup cameraof the vehicle.

The CPU 112 and the power supply 110 are coupled to I/O (Input-Output)port 128, which provides an interface that is configured to receiveinput from (and/or provide output to) networked devices 131. Thenetworked devices 131 can include any device (including test equipment)capable of point-to-point and/or networked communications with thecomputing device 100. The computing device 100 can be coupled toperipherals and/or computing devices, including tangible, non-transitorymedia (such as flash memory) and/or cabled or wireless media. These andother such input and output devices can be selectively coupled to thecomputing device 100 by external devices using wireless or cabledconnections. The storage 114 is accessible, for example, by thenetworked devices 131. The CPU 112, storage 114, and power supply 110are also optionally coupled to an external power source (not shown),which is configured to receive power from a power source (such as abattery, solar cell, “live” power cord, inductive field, fuel cell,capacitor, and energy storage devices).

The transducer controller 138 includes control and signaling circuitrycomponents for resonating a transducer of the lens cover system 132,such that the lens element can be cleaned by expelling foreign material(e.g., shaken clean of moisture). As described hereinbelow, thetransducer controller 138 includes a temperature calculator 140 fordetermining a temperature of the lens cover system 132, such that, forexample, the transducer of the lens cover system 132 is operated withina safe range of operating parameters.

FIG. 2 is a cross-section view of an example camera lens cover system.The camera lens cover system 200 generally includes a lens element 220,a seal 230, a housing 240, a transducer 250, and a camera 260. Thecamera 260 includes a camera lens 262, a camera base 264, aphotodetector 272, and controller circuitry 274. The transducer 250 isoperable to vibrate at a selected frequency (such as a factory-selectedfrequency or an operator-selected frequency) for motivating thedispersal of the moisture 210 (or other foreign materials) from theexterior (e.g., upper) surface of the lens element 220.

The lens element 220 is a transparent element elastically captivated ina distal (e.g., upper) portion of the housing 240. The lens element 220is arranged to receive light from surrounding areas and to opticallycouple the received light to the photodetector 272 (e.g., via the cameralens 262). The lens element 220 is arranged to protect the camera lens262 against moisture 210 intrusion, for example. The moisture 210 can bein the form of frost, water drops, and/or a film of condensation.Foreign materials (such as the moisture 210 and dirt particles) canblock and/or diffuse light, such that at least some of the receivedlight is prevented from reaching the camera lens (e.g., compound lens)262. In an embodiment, the lens element 220 can be a focusing lens(e.g., for refractively focusing light).

A seal 230 (such as a rubber seal) is arranged to elastically captivatethe lens element 220 to the housing 240 and to seal a cavity (e.g., inwhich the camera lens 262 is arranged) against intrusion of moisture 210into the cavity. The intrusion of moisture 210 and other foreignsubstances into the cavity can facilitate condensation inside the lenscover system that can obstruct the camera's view. Moisture inside thelens cover system can also damage the controller circuitry 274electronics and/or the pixels (e.g., pixel cells) of the photodetector272. The cavity extends inwards from the lens element 220 to a proximal(e.g., lower) portion of the housing 240.

The cavity is also formed by the camera base 264, which is coupled to(or formed as part of) the housing 240. The camera base 264 can includea photodetector 272 and controller circuitry 274. The photodetector 272can be a video detector for generating electronic images (e.g., videostreams) in response to the focused light coupled through the lenselement 220 and the camera lens (which can include lenses). Thecontroller circuitry 274 can include: (a) a printed circuit board; (b)circuitry of the transducer controller 138; and (c) and the circuitry ofthe temperature calculator 140 for controlling the lens cover system 132(e.g., where such circuitry and the lens cover system are arranged in afeedback loop structure). The controller circuitry 274 is coupled toexternal power, control, and information systems using wiring and/oroptical conduits (such as fibers).

The transducer 250 is mechanically coupled to the lens element 220. Thetransducer 250 can be affixed to the lens element 220 by an interveningadhesive layer (e.g., a high-temperature resistant epoxy). In operation,the transducer 250 is arranged to vibrate (e.g., at a selectedfrequency) the lens element 220 in response to transducer driversignals. The transducer driver signals are controllably modulated, suchthat the transducer 250 is controllably excited in response to thetransducer driver signals. The transducer driver signals can beamplitude modulated, such that vibrating lens element 220 cancontrollably expel moisture 210 and other such foreign material from theexternal surface of the lens element 220 (e.g., external to the cavity).

A lens cover system 132 can include the transducer 250, the housing 240,the seal 230, and the lens element 220. As described hereinbelow, thecomputing device 100 estimates the temperature of the lens cover systemin response to (e.g., as a function of) electrical properties of thelens cover system. The computing device 100 controllably excites thetransducer 250 in response to the estimated temperature to efficientlyremove obscuring foreign material (including potentially obscuringforeign material) from the lens element 220 without exceed a thresholdtemperature limit. (For example, the transducer 250 can be destroyed ordegraded when operated for prolonged periods at excessively elevatedtemperatures.)

The impedance response of the lens cover system 132 varies according tothe temperature of the lens cover system 132. As described herein, therelationship between the estimated temperature of the lens cover system132 and the measured electrical impedance of the lens cover system issubstantially linear within a frequency range. FIG. 3, as describedhereinbelow, shows an impedance response of an example lens cover systemover a frequency range of selected temperatures.

FIG. 3 is a waveform diagram of an impedance response of an example lenscover system over a broad frequency range. The waveform diagram 300includes a lens cover system impedance response 310. The lens coversystem impedance response 310 shows the impedance in Ohms over afrequency range between 10 kHz to around 1 MHz. The example lens coversystem can be a lens cover system, such as the system 200 describedhereinabove.

The “zeros” of the impedance response correspond to the series resonanceproperties, which correspond to the electromechanical vibrationproperties (such as resonance) of a lens cover system that includes theexample transducer. The electromechanical resonances of the system occurat frequencies in which relatively larger vibration amplitudes occur fora variable electrical input amplitude stimulus. For example,electromechanical resonances occur at frequency ranges 321, 322, and323. The zeros are indicated by valleys (such as valley 301) in thecurve 310. A reduced frequency range (e.g., for a “zoomed in” view) ofthe impedance response 310 is described hereinbelow with respect to FIG.4.

FIG. 4 is a waveform diagram of an impedance response of an example lenscover system over a reduced frequency range. The waveform diagram 400includes an example lens cover system impedance response 410. The lenscover system impedance response 410 shows the impedance response of theexample lens cover system over a reduced frequency range (e.g., withrespect to the frequency range shown in FIG. 3).

The lens cover system impedance response 410 includes discretetemperature curves for indicating the lens cover system impedance at adiscrete temperature selected from a range of temperatures. The range ofselected discrete temperatures extends from a temperature of − (minus)40° C. to a temperature of 60° C., where the temperature represented byeach temperature curve differs from the represented temperature of anadjacent temperature curve by 20° C. The range of temperaturesencompasses operating temperatures potentially encountered in operationof the example lens cover system in various example applications.

For example, the temperature curve 412 shows the example lens coversystem impedance response in Ohms over a frequency range of around 20kHz to 40 kHz at a temperature of −40° C., whereas the temperature curve414 shows the lens cover system impedance response in Ohms over afrequency range of around 20 kHz to 40 kHz at a temperature of 60° C.The lens cover system impedance response 410 includes a valley 401,which indicates a resonance of the example lens cover system at around29 kHz for all illustrated temperature responses.

At frequencies below 150 kHz (e.g., as shown by the lens cover systemimpedance response 310), the gain of an impedance response generallydecreases as the temperature increases, such that the gain of the lenscover system impedance response 410 is inversely related to temperaturewithin a selected operating frequency range (e.g., with exceptionsoccurring around the locations of resonant frequencies of the exampletransducer). The change in the impedance over temperature is linear(e.g., having a constant slope and having a change in impedance that isproportional to a step change in temperature).

For example, the vertical spacing (e.g., for a given frequency) betweeneach temperature curve between temperature curves 412 and 414 of aselected operating frequency is equal (e.g., substantially equal). Theselected operating frequency is selected from a frequency included in alinear response region, such as the linear response region extendingbetween, at least, 20 kHz and 25 kHz). The equal spacing of thetemperature curves between temperature curves 412 and 414 is indicativeof a linear relationship between an operating temperature and a measuredimpedance at a selected operating frequency.

The computing device 100 determines temperature of the exampletransducer in response to a measurement of the impedance of the exampletransducer. For example, the computing device 100 excites the exampletransducer to vibrate (e.g., in response to amplitude-modulated driversignals) at a frequency within a frequency range, so the transducerimpedance varies linearly as a function of the frequency within at leastpart of the frequency range.

The dependent variable temperature T as a function of the impedancevariable Z for the example transducer is expressed as the linearequation:

T=−0.29*Z+392.6  (1)

which has a coefficient of determination R² value of R²=0.9932 (e.g.,which is substantially linear, and wherein the constant “−0.29” is aslope of the linear equation, and the constant “392.6” is a y-interceptof the linear equation). The dependent variable temperature T as afunction of the impedance variable Z for the example transducer can alsobe expressed as the parabolic equation:

T=A*Z ² +B*Z+C  (2)

where A, B and C are constants. When A=0, Equation (2) is reduced to thelinear form (such as the form of Equation (1)). Accordingly, theselected operating frequency is selected from within a frequency regionwithin which the relationship between the estimated temperature and themeasured impedance is determinable as a quadratic function (e.g.,according to the Equation (2)).

The determined relationship between the estimated temperature of thelens cover system and the actual (e.g., empirically measured)temperature of the example lens cover system is substantially linearwhen the coefficient of determination R² value is at least 0.95, forexample. As the value of the coefficient of determination R² approachesunity, the statistical variance between an estimated value using thelinear equation and the actual value is minimized. As the value ofcoefficient of determination recedes from unity, errors in theestimation increase, which can result in any of: (a) decreasedtemperature operating range; (b) increased safety margins; and (c)decreased life of the lens cover system.

FIG. 5 is a plot diagram showing a linear relationship between theimpedance response of an example lens cover system and operatingtemperatures thereof while operating at a selected operating frequencyof 20 kHz. As described herein, the computing device 100 estimates theoperating temperature of a lens cover system by measuring the impedanceof the lens cover system at a selected operating frequency, and byconverting the impedance measurement to an estimated temperature (e.g.,according to the relationship described by Equation (1) hereinabove).The computing device 100 executes the conversion of the impedancemeasurement to an estimated temperature in response to calculating theEquation (1) result, and/or by indexing a lookup table to retrieve aresult according to Equation (1).

Plot 500 shows the close statistical correlation between estimated curve520 (EST) and a corresponding empirically measured curve 510 (MEAS). Theactual (e.g., simulation value of) temperature is shown by theempirically measured curve 510. The estimated temperature (e.g.,calculated using Equation (1)) is shown by the estimated curve 520. Thecomputing device 100 estimates the curve 520 in simulations bycontrolling the temperature (e.g., from −60° C. to 40° C.) to deriveimpedance measurements (e.g., ranging from around 1150 Ohms to 1475ohms) of the example lens cover system. The empirically measured curve510 and the estimated curve 520 are statistically correlated to a highdegree.

As shown by the plot 500, the relationship between the estimatedtemperature of the lens cover system and the actual (e.g., empiricallymeasured) temperature of the example lens cover system is linear (e.g.,substantially linear). The maximum error (e.g., determined insimulations between corresponding points of the estimated curve 520 andthe empirically measured curve 510) shown by plot 500 is 3.7° C.Accordingly, the computing device 100 accurately estimates the lenscover system temperature using a simple linear equation.

For example, a temperature error 3.7° C. of a temperature estimate issufficiently accurate, such that the example lens cover system can besafely operated when the transducer controller maintains the estimatedoperating temperature of the example lens cover system below atemperature threshold for estimated temperatures. As describedhereinbelow, the computing device 100 selects the operating temperaturethreshold for estimated temperatures in response to the error margin ofthe estimated temperature measurement and the Curie temperature of theexample transducer. The Curie temperature threshold can be a temperaturethreshold beyond which the permanent polarization of piezoelectricmaterials of the example transducer is degraded (for example, the Curietemperature threshold can be half of the Curie temperature).Accordingly, the temperature threshold is for delineating an operatingtemperature range (such as by delineating an upper and/or lower limitthereof), below which the example transducer can be activated withoutdepolarization (e.g., accelerated depolarization).

In an embodiment, the computing device 100 measures the impedance dataover a range of temperatures for a selected operating frequency atdiscrete temperatures, and the computing device 100 stores that data asa lookup table in memory (e.g., which reduces processing requirementsfor calculating the equation otherwise calculated to determine aninstant operating temperature). The computing device 100 performs linearinterpolation (e.g., one-dimensional linear interpolation) to moreprecisely determine the operating temperature (e.g., depending on aparticular application of the described techniques, such as measuring atemperature outside a vehicle for determining a control decisiondescribed hereinbelow).

In an embodiment, the computing device 100 stores impedance datameasured over a range of temperatures and over a range of operatingfrequencies. The computing device 100 measures impedance data atdiscrete temperatures and discrete operating frequencies, and thecomputing device 100 stores that data as a lookup table in memory (e.g.,such that programmed firmware is not required for controlling specifictransducers, each of which is operable at mutually different frequenciesaccording to a selected transducer and a selected application). Thecomputing device 100 performs linear interpolation (e.g.,two-dimensional linear interpolation) to more precisely determine theoperating temperature for a selected operating frequency.

FIG. 6 is a flow diagram of an example process for estimating atemperature of an example lens cover system in response to an impedancemeasurement of the example lens cover system. The computing device 100can perform the flow 600 by hardware circuits exclusive of programmingcommands. For example, the example process can be executed by apparatusincluding analog and/or digital control circuits (such as registers,adders, multipliers, voltage generators, and comparators) that arearranged (e.g., pipelined) according to the process 600, describedhereinbelow.

The flow 600 begins at operation 610, at which an example transducer isactivated (e.g., electrically excited at a selected frequency byassertion of amplitude-modulated transducer driver signals). Forexample, the amplitude-modulated transducer driver signals are assertedto effect excitation of the example lens cover system at the selectedfrequency of 20 kHz (which is a frequency at which a linear relationshipexists between the temperature of the example lens cover system and theimpedance of the lens cover system). The flow continues to operation620.

At operation 620, the impedance (e.g., effective impedance) of theactivated example lens cover system is measured. In an examples, thecomputing device 100 measures impedance in response to a voltage dropresulting from coupling the example transducer to the assertedamplitude-modulated transducer driver signals. Because the example lenscover system is excited at 20 kHz, the measured impedance is derived inresponse to example transducer excitation at the selected frequency of20 kHz. The flow continues to operation 630.

At operation 630, the measured impedance is converted to an estimatedtemperature. The estimated temperature is determined according to thelinear relationship between the impedance of the example lens coversystem and the operating temperature of the example lens cover system.For example, the computing device 100 converts the measured impedance tothe estimated temperature by circuits operating according to thefunction of Equation (1), and/or the computing device 100 converts themeasured impedance to the estimated temperature in response to indexinga lookup table with values for creating the output of Equation (1). Thelookup table includes values that are addressable using the independentvariable (e.g., the measured impedance) as the index, and that areoutput as results for providing or determining the value of thedependent variable. For example, the addressable values are determined(e.g., pre-calculated before or after deployment of the system 100)according to Equation (1). The flow continues to operation 640.

At operation 640, the temperature is compared against a temperaturethreshold. The computing device 100 determines temperature threshold inresponse to the Curie temperature threshold and a safety margin. Thecomputing device 100 selects safety margin in response to the Curietemperature threshold, the maximum expected error of the estimated lenscover system temperature, and a margin for “derating” the lens coversystem for increasing product lifetime (e.g., increasing themean-time-between-failure reliability factor) of the example lens coversystem. The flow continues to operation 650.

At operation 650, the activation state of the transducer is toggled(e.g., activated when the example transducer is in a deactivated state,or is deactivated when the example transducer is in an activated state)in response to the comparison at operation 640. For example, the exampletransducer is deactivated if the temperature indicates that the examplelens cover system has an operating temperature that approaches aself-damaging temperature. The computing device 100 deactivates theexample transducer when the comparison at operation 640 indicates thatthe estimated temperature exceeds half of the Curie temperature (indegrees Celsius) of the example transducer.

The computing device 100 performs the process 600 each time the exampletransducer is activated. For example, the computing device 100 may limitthe length of a periodic interval (e.g., fixed period) of time duringwhich the example transducer is activated, in order to periodicallyreperform the process 600 and thereby limit the accumulation of heatthat results from activation of the example transducer. The computingdevice 100 deactivates the example transducer in response to expirationof a fixed period of time during which the example transducer isactivated. The computing device 100 selects the length of time forlimiting activation of the example transducer, in view of the rate ofaccumulation of heat during operation at the selected operatingfrequency and the relative sizes of safety margins. Accordingly, thecomputing device 100 controllably limits the rise of temperature of theexample lens cover system, below levels that are likely to permanently(e.g., without repair) damage the example transducer (e.g., withoutincurring the space, cost and reliability considerations otherwiseencountered by coupling a thermocouple to the example transducer).

FIG. 7 is an isometric view of an example camera lens cover system. Thecamera lens cover system 700 generally includes a transducer 710, powerwires 720, a lens element 730 and bonding agent 740. The transducer 710of the camera lens cover system 700 can be a cylindrical transducer,such as transducer 250 described hereinabove, which is arranged to applyultrasonic vibrations for cleaning and/or heating a camera lens cover.

The transducer 710 is arranged to vibrate a mechanically coupled lenscover (e.g., the lens element 730) in response to being driven by anelectronic amplifier at frequencies ranging from around 20 kHz to 2.0MHz. The computing device 100 can drive the transducer 710 at a givenexcitation frequency, and the computing device 100 can sense a resultingimpedance by coupling signals to and from the transducer via the powerwires 720. The resulting impedance can be affected by temperature,mechanical characteristics, electrical characteristics and the frequencyat which the transducer is driven, for example. A lens element 730 issecured to a distal surface of the transducer 710 by a bonding agent 740(e.g. epoxy) disposed (e.g., as a circular shape) between the distalsurface of the transducer 710 and an adjacent portion of a surface ofthe lens element 730. The seal between the transducer element and thelens element 730 helps prevent the intrusion of moisture into a sealedcavity (e.g., which can be formed by a camera base, the transducer 710,the lens element 730, and the bonding agent 740).

Environmental moisture (e.g., water drops, water droplets and/or a filmof condensation) can adhere to an exterior surface of the lens element730. The moisture can occlude light from being clearly received by acamera lens in the sealed cavity. The transducer 710 is operable tovibrate at a selected frequency for motivating the dispersal of themoisture (or other foreign materials) from the exterior (e.g., outer)surface of the lens element 730. When droplets of moisture and/or a filmof condensation remain on the exterior surface of the lens element 730,the remaining moisture can cause saturation of the image sensoroptically coupled to the camera lens when, for example, incident lightencounters the exterior surface of the lens element 730 at an obliqueangle.

The exterior surface of the lens element 730 can be formed without a“lip” (or can be formed with a lip arranged with channels extendingtherethrough), which provides a path for moisture migration duringvibration. For example, vibration of the sealed lens element urgesmoisture along the path for moisture migration, because the vibrationhelps overcome surface tension of the moisture (which otherwise helpsthe moisture to adhere to itself and to the outer surface of the lenselement 730). As described hereinbelow with respect to FIG. 8, thetransducer 710 is arranged to (e.g., both) vibrate at the selectedfrequency and to generate thermal energy for heating the lens element730.

FIG. 8 is an external view of foreign contaminant volumes for an examplecamera lens cover system. Water drops “contaminate” a lens surface(e.g., of lens element 730), such that a view through the lens surfaceis blocked or otherwise obscured. In an example, a camera lens coversystem is vertically oriented, such that the lens element 730 is level,and such that moisture is not removed by gravity (e.g., for the purposeof illustration) during the moisture removal stages 810, 820, and 830.In the example, the multi-stage cleaning diagram 800 includes alarge-volume cleaning stage 810 (e.g., for generally removing dropsgreater than around 15 μL in volume, such as drop 812), a medium-volumecleaning stage 820 (e.g., for generally removing drops less than around15 μL in volume, such as drop 822), and a small-volume cleaning stage830 (e.g., for removing residual moisture, such as droplets 832).Accordingly, a size of a foreign material is reduced by vibrating thelens element in the large-volume cleaning stage 810, the size of theforeign material is further reduced by vibrating the lens element in themedium-volume cleaning stage 820, and the size of the foreign materialis even further reduced by vibrating the lens element in thesmall-volume cleaning stage 830.

In the large-volume cleaning stage 810, the transducer is arranged tovibrate in a first mode at a first selected frequency such that waterdrops of around 4-10 mm (or greater) diameter are dispersed (e.g.,atomized or otherwise reduced in size) in response to vibrationgenerated at the first selected frequency. In the first mode (in stage810), a large-volume cleaning excitation signal is applied to thetransducer to generate vibration at the first selected frequency. Thefirst selected frequency can be a frequency in a frequency range atwhich electromechanical resonances occur. The first selected frequencycan be characterized by a relatively high frequency vibration thatconsumes a relatively high amount of power. The large-volume cleaningstage 810 can be followed by the medium-volume cleaning stage 820.

In the medium-volume cleaning stage 820, the transducer is arranged tovibrate in a second mode at a second selected frequency, such that waterdrops (or droplets) of around 1-4 mm diameter are dispersed (e.g.,atomized or otherwise reduced in size) in response to the vibrationgenerated at the second selected frequency. In the second mode (in stage820), a medium-volume cleaning excitation signal is applied to thetransducer to generate vibration at the second selected frequency. Thesecond selected frequency can be a frequency in a frequency range atwhich electromechanical resonances occur. The second selected frequencycan be a frequency that is lower than the first selected frequency. Thefirst selected frequency can be characterized by a relatively lowfrequency vibration that consumes a relatively low amount of power. Themedium-volume cleaning stage 810 can be followed by a small-volumecleaning stage 830.

In the small-volume cleaning stage 830, the transducer is arranged tovibrate in a third mode at a third selected frequency, such that waterdroplets of around 0-1 mm diameter are evaporated (e.g., atomized orotherwise dispersed) in response to the heat and vibration generated atthe third selected frequency. In the third mode (in stage 830), aheating excitation signal is applied to the transducer to generatevibration at the third selected frequency. The third selected frequencycan be a frequency in a frequency range at which electromechanicalresonances occur. For example, the water droplets of around 0-1 mmdiameter are difficult to remove by vibrations, because of the water'ssurface tension and because of the relatively high van der Waals forcesexerted between the surface of the lens cover and the water.

The third selected frequency can be a frequency that is higher than thefirst selected frequency. The third selected frequency can becharacterized by a relatively high frequency vibration that consumes arelatively high amount of power. The heat generated by the transducer isthermally coupled to the lens element via the bonding agent 740interposed between the transducer 710 and the lens element 730. The heattransferred to the lens element 730 helps remove any residual droplets,condensates on the lens element.

A control system described hereinbelow with respect to FIG. 9 isarranged to control the amount of heat generated so as to not overheatthe piezoelectric material (which can damage the transducer actuator)and to avoid exceeding safe touch temperatures on the surface of thetransparent element 730. The computing device 100 estimates thetransducer temperature by measuring the impedance of the lens coversystem as described hereinabove.

FIG. 9 is a block diagram of an example signal generator of an examplecamera lens cover system. For example, the signal generator 900 isarranged to control signals for driving a transducer of the lens coversystem, to monitor the transducer performance and to change aspects ofthe drive signals in response to the monitored transducer performance.

The signal generator 900 includes a voltage (V) boost circuit 902 thatis arranged to receive power (such as 12 volts direct current input froma vehicle power system) and to generate a 50-volt potential (e.g.,surge-protected potential) from the received 12-volt input power. The50-volt potential is modulated as described hereinbelow for driving atransducer of the camera lens cover system.

The signal generator 900 also includes an embedded core (such as amicrocontroller unit MCU) 910 for executing instructions to transformthe embedded core into a special-purpose machine for executing thefunctions of the camera lens cover system controller 920. For example,the camera lens cover system controller 920 includes control algorithms922, pulse-width modulation (PWM) signal generation circuit 924,temperature estimation and regulation circuit 926 and system monitoringand diagnostics circuit 928. Such functions are described hereinbelowwith respect to FIG. 10.

The camera lens cover system controller 920 is arranged to selectoperating parameters (such as cleaning modes, heating modes, cleaningstages, frequencies and operating temperatures) for the camera lenscover system in response to monitoring the camera lens cover systemtransducer and to control the PWM switching controller 930 in responseto the selected operating parameters. For example, the camera lens coversystem controller 920 is arranged to control PWM switching times of thePWM switching controller 930. The PWM switching controller 930 isarranged to signal the PWM PreDriver 940 in response to the switchingtimes received from the PWM switching controller 930. The PWM PreDriver940 generates control signals for toggling (e.g., actuating) theswitches of the Class D driver 950. The Class D Driver 950 is afull-bridge rectifier that is arranged to generate +/−50 volts (e.g.,100 volts peak-to-peak) for driving the transducer 960. The sensecircuitry 970 generate current and voltage signals for sensing impedanceof the camera lens cover system and transducer 960, which are monitored(e.g., buffered) by the transducer monitor 980. The monitor signals arecoupled via a multiplexer (MUX) 990 to the analog-to-digital converter(ADC) 990 for sampling. The embedded core 910 is arranged to receive thesampled current and voltage signals, to compute (via the camera lenscover system controller 920) new PWM signaling, to perform temperatureestimation and regulation and to perform system monitoring anddiagnostics as described hereinbelow with respect to FIG. 10.

FIG. 10 is a flow diagram 1000 illustrating an example method, performedby the computing device 100, of foreign contaminant removal from anexposed surface of the example camera lens cover system describedherein. At 1002, the process begins in the camera lens cover systemcontroller described hereinabove. At 1010, the camera lens cover systemcontroller waits a period of time (e.g., waits for the system startsignal) before identifying and/or determining the existence (presence)of contaminants at 1014. If the wait duration is not expired, the waitduration is updated at 1012, and the process loops back to 1010.

At 1014, after the wait period has expired, a frequency measurementdevice monitors the resonant frequency the example camera lens coversystem to identify (for example) the amount of contaminant disposed onthe exposed surface. For example, the computing device 100 determinesthe amount of a contaminant in response to a measured frequency responseof the camera lens cover system and comparing the measured frequencyresponse to a database that includes known frequency responses for giventypes and amounts for specific contaminants. At 1020, the camera lenscover system controller determines whether a contaminating materialexists (is present) on the camera lens cover, such that at least oneoperation for cleaning the camera lens cover is initiated. If “YES,”then at 1028, the temperature of the example camera lens cover system isdetermined, and types of cleaning and heating are selected in responseto the determined temperature as described hereinbelow. If “NO,” thensystem checks are performed at 1030.

If at 1020 the presence of a material is not indicated (“NO”), then at1030, the process initiates system monitoring and diagnostics tests(e.g., during which the camera lens cover system is self-tested). At1032, the computing device 100 decides whether to disable the system.For example, the computing device 100 decides whether to disable thesystem, in response to the nature of faults diagnosed at 1030, aresponse to a user input and/or a response to whether the power has beenturned off to the system. If the system is to be disabled (“YES”), thenat 1034, the system is shut down. If the system is not to be disabled(“NO”), the process loops back to 1010 and waits for a specifiedduration before the process starts again.

As described hereinabove, at 1028, the temperature of the example cameralens cover system is determined. For example, the computing device 100determines the temperature of the example camera lens cover system inresponse to (e.g., as a function of) an operating frequency of anactivated transducer as described hereinabove, or by a temperaturesensing device (such as an externally coupled thermocouple). The processcontinues at 1050, for example.

If at 1050 the determined temperature is below the freezing point ofwater (e.g., within a margin of error), then at 1052, the camera lenscover system controller generates a heating signal for a specifiedduration (e.g., time period). For example, in response to a comparisonof the determined temperature to the freezing point of water, the cameralens cover system controller can generate a heating excitation signal ina selected heating mode for warming the camera lens cover system asdescribed hereinabove by exciting the transducer at a frequency at whichthe transducer generates relatively large amounts of heat, which occursat frequency locations where the impedance response is small for a givenvoltage input. For example, the heating excitation signal in a heatingmode for warming the camera lens cover system can be generated at avalley (such as the valley of the frequency range 321, which includes arelatively low impedance value of a selected frequency range) of a lenscover system impedance response curve (such as described hereinabovewith respect to FIG. 3 and FIG. 4).

At 1054, the temperature of the example camera lens cover system isdetermined. After the temperature is determined (e.g., after initiationof a heating or cleaning mode), the process continues at 1040, afterwhich the process initiates further operations (described hereinbelow)to ensure, for example, the transducer is operated within a safeoperating region of temperatures.

If at 1056 the type and size of detected contaminating materialindicates the contaminating material is to be reduced in size, then at1058, a cleaning signal is generated for cleaning the example cameralens cover system. For example, the camera lens cover system controllercan select a cleaning mode in response to the size of detectedcontaminating material. In selecting the cleaning mode, the computingdevice 100 can generate the cleaning signal as one of a large-volumecleaning excitation signal, a medium-volume cleaning excitation signaland a small-volume cleaning excitation signal. For example, thecomputing device 100 can generate: the large-volume cleaning excitationsignal at a frequency conducive to resonating larger size drops ofwater; the medium-volume cleaning excitation signal at a frequencyconducive to resonating medium size drops of water; and the small-volumecleaning excitation signal at a frequency conducive to heating smalldroplets of water. After the large-volume or medium-volume cleaningsignal is generated and applied at 1058, the process continues to 1054at which the computing device 100 determines the temperature of theexample camera lens cover system (e.g., to ensure, the transducer isoperated within a safe operating region of temperatures).

For example, if the size of detected contaminating material indicatessmall droplets of water at 1060, such that drying is indicated, then aheating signal is generated at 1062 for cleaning the example camera lenscover system. For example, the camera lens cover system controller cangenerate a heating signal in a heating mode, such that water droplets ofaround 0-1 mm diameter are evaporated (e.g., atomized or otherwisedispersed) in response to the heat and vibration generated, in responseto the heating signal (e.g., applied at a frequency different from therespective frequencies of the applied cleaning signals). After theheating signal is generated and applied at 1062, the process continuesat 1054 where the computing device 100 determines the temperature of theexample camera lens cover system (e.g., to ensure, the transducer isoperated within a safe operating region of temperatures).

After the temperature is determined (e.g., again) at 1054, the processcontinues at 1040, where the computing device 100 determines whether thetemperature of the example camera lens cover system exceeds atemperature threshold. For example, the temperature threshold can behalf of the transducer Curie temperature, such that the transducer iscontrolled to operate within a safe temperature range. If “YES,” thecomputing device 100 proceeds to disable the applied signal (e.g.heating or cleaning signal) at 1042. At 1044, the computing device 100initializes cooling of the transducer and/or exposed surface (e.g., byentering a delay period during which the heating or cleaning signal isdisabled, such that additional heat is not generated). At 1046, thecomputing device 100 determines the latest temperature, and in responseat 1048, the computing device 100 determines whether the transducertemperature has finished cooling. For example, the computing device 100can make the decision in response to the information determined at 1046,such that the temperature can be determined to be below a selectedtemperature threshold. In an example, the temperature threshold can behalf of the transducer Curie temperature, such that the transducer iscontrolled to operate within a safe temperature range. In anotherexample, the temperature threshold can be less than the transducer Curietemperature. If “YES” (e.g., when finished cooling), then at 1048, theprocess loops back to 1010. If “NO,” then at 1048, the process loopsback to 1046, the computing device 100 determines a latest temperature,and the process loops back to 1048 (e.g., for additional cooling).

If “NO” at 1040 (e.g., when the transducer temperature does not exceedthe temperature threshold), then at 1016, the computing device 100determines whether the cleaning process is complete. If “YES,” then theprocess starts again at 1010. If “NO” at 1016, then at 1018, thecomputing device 100 updates the cleaning signal duration, and theprocess loops back to 1020 for additional testing and potential cleaningoperations.

FIG. 11 is a waveform diagram of an impedance response of an examplelens cover system across a broad frequency range. The waveform diagram1100 includes a lens cover system impedance response 1110 and a phaseresponse 1120. The lens cover system impedance response 1110 shows theimpedance in Ohms across a frequency range between 10 kHz to around 1MHz. The lens cover system phase response 1120 shows the phase shift indegrees across the frequency range between 10 kHz to around 1 MHz. Theexample lens cover system can be a lens cover system, such as the system200 described hereinabove.

The “zeros” of the impedance response across a range of operatingfrequencies of the system correspond to series resonance properties ofthe example lens cover system. The series resonances of the system occurat frequencies in which relatively larger vibration amplitudes occur(and in which greater amounts of heat are generated within thetransducer) for a variable electrical input amplitude stimulus. Forexample, electromechanical resonances occur at frequency ranges 1103,1104, 1105 and 1106. The zeros are indicated by valleys (such as valleys1113, 1114, 1115 and 1116) in the curve 1110. The computing device 100selects the frequency range (and a valley therein) for assertion of aheating signal, in response to determining the magnitude (e.g., lowestmagnitude) of an impedance across a range of possible operatingfrequencies. The computing device 100 selects a heating mode (e.g.,frequency of a heating signal) in response to a determination of avalley of series resonances of the apparatus, wherein the seriesresonances are measured by the controller circuitry at variousfrequencies selected from a range of operating frequencies. Accordingly:(a) the computing device 100 measures an impedance-versus-frequencycurve (e.g., 1110) in response to vibrating the lens element across arange of operating frequencies (e.g., 10 kHz through 1 MHz); (b) withinthat impedance-versus-frequency curve, at least one particular frequencyof that vibration causes a respective valley (e.g., 1115) in themagnitude of the impedance; (c) a respective fixed bandwidth (e.g.,frequency range 1105) encompasses that particular frequency; and (d) atleast one example frequency of the heating signal is selected fromwithin that respective fixed bandwidth.

The zeros are also characterized by relatively large phase shifts (suchas a phase shift of over 100 degrees), wherein the instantaneousmagnitude of the phase shift indicates the relative frequency locationbetween a zero (at a lower frequency) and a pole (at a higher frequency)across a range of operating frequencies that includes: a phase peak; aproximate zero (e.g., the zero proximate to the phase peak); and aproximate pole (e.g., the pole proximate to the phase peak). The phasepeaks 1123, 1124, 1125 and 1126 each occur within a respective relativefrequency range 1103, 1104, 1105 and 1106, where each respectiverelative frequency range includes a valley (e.g., 1113, 1114, 1115 and1116, respectively).

The computing device 100 detects the proximate zero associated with eachof the phase peaks 1123, 1124, 1125 and 1126 by sweeping the operatingfrequency (e.g., downwards from a highest operating frequency). Duringthe frequency sweep, the computing device 100 determines the phase peaksby tracking the resulting phase shift (e.g., by CPU 112 receivingsignals from an ADC or a zero crossing detector). For example, as shownin FIG. 11, the frequency range 1105 includes: (a) a zero 1115 along thecurve 1110; and (b) its associated phase peak 1125 along the curve 1120.Further, as shown in the example of FIG. 11, a frequency of theassociated phase peak 1125 is approximately midway between: (a) the zero1115; and (b) a pole of the curve 1110 within the frequency range 1105.In an example, the computing device 100 estimates the frequency of theproximate zero (e.g., at 1115) by: (a) evaluating an acceleration of thephase shift response 1120 across a lower frequency skirt (e.g., leftskirt) of its associated phase peak (e.g., 1125); and (b) in response tothat evaluating, determines such lower frequency skirt's inflectionpoint (e.g., a point of a 45 degree slope). Accordingly, the computingdevice 100 selects the frequency of the heating signal from within afixed bandwidth (e.g., frequency range 1105) that encompasses both theassociated phase peak (e.g., 1125) and its lower frequency skirt'sinflection point.

The computing device 100 determines relative impedances of variousfrequencies (e.g., estimated zeros) in response to comparisons oftemperature measurements of heating generated by applied heating signalsat different operating frequencies (although the different operatingfrequencies at which the heating signals are applied need not beassociated with an estimated zero). For example, the computing device100 can apply the heating signal at a frequency associated with at leastone estimated zero, such that the computing device 100 determines therelative efficiency of the heating signal at the frequency associatedwith the estimated zero. The computing device 100 determines relativeefficiency of the heating signal at the frequency associated with theestimated zero, by measuring a difference in temperatures sampled beforeand after the application of the heating signal. When temperaturedifferences are determined for each of multiple zeros, the computingdevice 100 selects the zero associated with the greatest temperaturedifference as being a heating signal frequency (e.g., where greatesttemperature difference indicates a low-impedance zero).

Accordingly, the computing device 100 selects a heating mode (e.g.,including frequency range and a valley thereof) for assertion of aheating signal, in response to the detection of at least one zero byanalysis of the phase response 1120. The selection of one of the lowermagnitudes impedances can help ensure faster generation of heat, suchthat an example camera lens cover system can be more quickly thawed. Thedetection of the low-impedance zero (e.g., instantaneous seriesresonance) can be dynamically (e.g., in use, after deployment and/or ina calibration routine) determined by an ADC (such as ADC 992, describedhereinabove) and a MCU (such as embedded core 910, describedhereinabove).

FIG. 12 is a top view of an example vehicle including example cameralens cover systems. The vehicle 1210 includes a vehicle body thatincludes an interior space sheltered from an exterior environment. Thevehicle 1210 includes at least one camera coupled to the vehicle body,where each camera includes a lens element, where the lens element istransparent and is exposed to the exterior environment. The vehicle alsoincludes at least one apparatus that includes a transducer arranged tovibrate the lens element at a selected operating frequency whenoperating in an activated state.

The vehicle 1210 further includes controller circuitry 1250 coupled tothe vehicle, wherein the controller circuitry 1250 includes a userinterface arranged to receive commands generated in response to anoperator operating the vehicle 1210 from the interior space of thevehicle, wherein the controller circuitry 1250 is arranged to measure animpedance of the apparatus while the transducer is operating at theselected operating frequency. The controller circuitry 1250 is arrangedto determine an estimated temperature of the apparatus in response tothe measured impedance and to generate a comparison of the estimatedtemperature of the lens element and/or transducer and a temperaturethreshold (e.g., for determining an operating mode and/or operatingtemperature range of the apparatus). The controller circuitry 1250 canalso toggle an activation state of the transducer in response tocomparing the estimated temperature of the apparatus against thetemperature threshold.

For example, when the estimated temperature indicates an ambienttemperature in which ice can exist, a heating signal is asserted beforeat least one cleaning signal is asserted. The heating signal can reducefrost into beads of water and/or vapor. The controller circuitry 1250reduces residual beads of water by asserting at least one cleaningsignal. Cleaning signals can be successively asserted at differentfrequencies by the controller circuitry 1250, such that larger beads ofwater are progressively reduced into smaller beads of water (asdescribed hereinabove). For example, the controller circuitry 1250asserts a heating signal as a drying signal to remove any residual beadsand/or a film of water on the surface of the lens cover (as describedhereinabove). The ambient temperature in which ice can exist can be atemperature at which ice (such as ice encountered on an example lenscover system) can remain frozen even after temperatures have risen abovea freezing point of water (e.g., at atmospheric pressures in which alens cover system is deployed). Accordingly, the controller circuitry1250 compares the estimated temperature using a temperature thresholdthat is determined (by the control circuitry 1250) in response to afreezing point of water, and in response to other factors, such as(thermal time unit) degree-seconds (e.g., as determined from atemperature log), thermal capacity, relative wind velocity and ambientlight.

In one example, the controller circuitry 1250 logs (e.g., samples atintervals and time stamps) temperature readings from lens cover systemimpedance measurements and/or other temperature sensors of the vehicle.Accordingly, the log of temperature samples includes information thatindicates whether any of the logged temperatures are within a range offreezing temperatures. The controller circuitry 1250 can determinewhether a likelihood exists of a presence of frost (e.g., frozenmoisture) on a cover of a lens element of a lens cover system inresponse to: an estimated ambient temperature; the extent and lengths oftime of the logged temperatures; analysis of an electronic imagegenerated in response to light traversing the lens element; margins oferror in temperature readings; and energies of phase change of waterfrom solid to liquid. The analysis can include determining contrastratios or other frequency information across all or some portions of theelectronic image, wherein predominantly low frequency information inselected areas indicates the presence of frost at lower temperatures(e.g., close to or below freezing temperatures). In response to anindication that frost exists, the controller circuitry 1250 can selectand assert a heating signal (such as described hereinabove with respectto operation 1052) to convert (e.g., thaw) frozen moisture on a lenselement of a lens cover system into residual moisture. (Accordingly, theresidual moisture includes previously frozen moisture.) The residualmoisture can be progressively reduced by vibration (e.g., at operation1058) and drying (e.g., any remaining residual moisture at operation1062).

The controller circuitry 1250 can be arranged to measure an impedance ofthe apparatus in response to commands received from the operatoroperating the vehicle from the interior space of the vehicle 1210. Thecontroller circuitry 1250 can also arranged to measure an impedance ofthe apparatus in response to the operator starting the vehicle 1210.

The controller circuitry 1250 includes a display 1260 (which can alsoinclude a touch screen) for displaying a synoptic view 1240 in responseto each video signal of a local view 1230 of a local camera (CAM) 1220.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. Apparatus, comprising: a lens element; atransducer to vibrate the lens element at a first frequency and adifferent second frequency; and controller circuitry to: determine anestimated temperature of the lens element; generate a comparison betweenthe estimated temperature and a temperature threshold; in response tothe comparison, activate the transducer to vibrate the lens element atthe first frequency to thaw moisture on the lens element; and activatethe transducer to vibrate the lens element at the second frequency toreduce a size of the thawed moisture.
 2. The apparatus of claim 1,wherein the controller circuitry is arranged to determine thetemperature threshold in response to a freezing point of water.
 3. Theapparatus of claim 2, wherein the transducer is arranged to reduce asize of a foreign material on the lens element by vibrating the lenselement at the second frequency, and the transducer is arranged tofurther reduce the size of the foreign material by vibrating the lenselement at a different third frequency.
 4. The apparatus of claim 3,wherein the foreign material includes moisture thawed in response to thelens element vibrating at the first frequency.
 5. The apparatus of claim4, wherein the controller circuitry is arranged to activate thetransducer to dry the lens element after reducing the size of theforeign material.
 6. The apparatus of claim 1, wherein the controllercircuitry is arranged to activate the transducer to dry the lens elementby vibrating the lens element at the first frequency after vibrating thelens element at the second frequency.
 7. The apparatus of claim 6,wherein the controller circuitry is arranged to generate the comparisonbetween the estimated temperature and the temperature threshold inresponse to logged temperatures.
 8. The apparatus of claim 7, whereinthe controller circuitry is arranged to select the first frequency inresponse to an electronic image generated in response to lighttraversing the lens element.
 9. The apparatus of claim 1, wherein thecontroller circuitry is arranged to toggle an activation state of thetransducer in response to determining the estimated temperature is belowa depolarization temperature of a piezoelectric material of thetransducer.
 10. The apparatus of claim 1, wherein the controllercircuitry is arranged to measure an impedance of the transducer and/orthe lens element, and to determine the estimated temperature in responseto the measured impedance.
 11. The apparatus of claim 10, wherein thecontroller circuitry is arranged to measure the impedance in response toan excitation of the transducer by a pulse-width modulated excitationsignal.
 12. The apparatus of claim 10, wherein the controller circuitryis arranged to determine the estimated temperature according to anequation T=A*Z²+B*Z+C, wherein Z is the measured impedance when thetransducer is activated, A is a constant, B is a constant, C is aconstant, and T is the estimated temperature.
 13. The apparatus of claim1, wherein the lens element is arranged to remove moisture from anexterior surface of the lens element when the transducer vibrates thelens element, by urging the moisture along a path for moisturemigration.
 14. A system, comprising: a vehicle including a vehicle body,wherein the vehicle body includes an interior space sheltered from anexterior environment; a camera coupled to the vehicle body, wherein thecamera includes a lens element that is transparent and is exposed to theexterior environment; apparatus including a transducer to vibrate thelens element at a first frequency and a different second frequency; andcontroller circuitry coupled to the vehicle, wherein the controllercircuitry is arranged to: determine an estimated temperature of the lenselement; select a heating mode in response to the estimated temperature;activate the transducer to vibrate the lens element at the firstfrequency in response to the controller circuitry selecting the heatingmode; and activate the transducer to vibrate the lens element at thesecond frequency in a cleaning mode after activating the transducer atthe first frequency in the heating mode.
 15. The system of claim 14,wherein the controller circuitry is arranged to determine the estimatedtemperature of the apparatus in response to an impedance of thetransducer and/or the lens element.
 16. The system of claim 14, whereinthe first frequency is within a fixed bandwidth that encompasses atleast one of: a frequency at which a valley exists in animpedance-versus-frequency curve; and an inflection point of a lowerfrequency skirt of a phase peak of a phase-versus-frequency curve;wherein the impedance-versus-frequency curve and thephase-versus-frequency curve are measured in response to vibrating thelens element across a range of operating frequencies.
 17. The system ofclaim 14, wherein the controller circuitry is arranged to select thefirst frequency in response to dynamically determining an instantaneousseries resonance of the transducer and/or the lens element.
 18. Thesystem of claim 17, wherein the controller circuitry is arranged toselect the first frequency in response to a determination of a frequencyof a phase peak measured in response to vibrating the lens elementacross a range of operating frequencies.
 19. A method, comprising:determining an estimated temperature of an apparatus, wherein theapparatus includes a lens element and a transducer; selecting a heatingmode in response to the estimated temperature; activating the transducerin the selected heating mode to vibrate the lens element at a firstfrequency to thaw moisture on the lens element; activating thetransducer in a cleaning mode to vibrate the lens element at a differentsecond frequency to reduce a size of the thawed moisture on the lenselement.
 20. The method of claim 19, wherein the estimated temperatureis estimated in response to an impedance measurement of the apparatuswhen the transducer is activated.